Hi Pavan, On Tuesday 06 Apr 2021 at 16:29:13 (+0530), Pavankumar Kondeti wrote: > In Android GKI, CONFIG_FAIR_GROUP_SCHED is enabled [1] to help prioritize > important work. Given that CPU shares of root cgroup can't be changed, > leaving the tasks inside root cgroup will give them higher share > compared to the other tasks inside important cgroups. This is mitigated > by moving all tasks inside root cgroup to a different cgroup after > Android is booted. However, there are many kernel tasks stuck in the > root cgroup after the boot. > > We see all kworker threads are in the root cpu cgroup. This is because, > tasks with PF_NO_SETAFFINITY flag set are forbidden from cgroup migration. > This restriction is in place to avoid kworkers getting moved to a cpuset > which conflicts with kworker affinity. Relax this restriction by explicitly > checking if the task is moving out of a cpuset cgroup. This allows kworkers > to be moved out root cpu cgroup. > > We also see kthreadd_task and any kernel thread created after the Android boot > also stuck in the root cgroup. The current code prevents kthreadd_task moving > out root cgroup to avoid the possibility of creating new RT kernel threads > inside a cgroup with no RT runtime allocated. Apply this restriction when tasks > are moving out of cpu cgroup under CONFIG_RT_GROUP_SCHED. This allows all > kernel threads to be moved out of root cpu cgroup if the kernel does not > enable RT group scheduling. OK, so IIUC this only works with cgroup v1 -- the unified hierarchy in v2 forces you to keep cpu and cpuset in 'sync'. But that should be fine, so this looks like a nice improvement to me. > [1] https://android.googlesource.com/kernel/common/+/f08f049de11c15a4251cb1db08cf0bee20bd9b59 > > Signed-off-by: Pavankumar Kondeti <pkondeti@xxxxxxxxxxxxxx> > --- > kernel/cgroup/cgroup-internal.h | 3 ++- > kernel/cgroup/cgroup-v1.c | 2 +- > kernel/cgroup/cgroup.c | 24 +++++++++++++++++++----- > 3 files changed, 22 insertions(+), 7 deletions(-) > > diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h > index bfbeabc..a96ed9a 100644 > --- a/kernel/cgroup/cgroup-internal.h > +++ b/kernel/cgroup/cgroup-internal.h > @@ -232,7 +232,8 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup, > int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, > bool threadgroup); > struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > - bool *locked) > + bool *locked, > + struct cgroup *dst_cgrp) > __acquires(&cgroup_threadgroup_rwsem); > void cgroup_procs_write_finish(struct task_struct *task, bool locked) > __releases(&cgroup_threadgroup_rwsem); > diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c > index a575178..d674a6c 100644 > --- a/kernel/cgroup/cgroup-v1.c > +++ b/kernel/cgroup/cgroup-v1.c > @@ -497,7 +497,7 @@ static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of, > if (!cgrp) > return -ENODEV; > > - task = cgroup_procs_write_start(buf, threadgroup, &locked); > + task = cgroup_procs_write_start(buf, threadgroup, &locked, cgrp); > ret = PTR_ERR_OR_ZERO(task); > if (ret) > goto out_unlock; > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 9153b20..41864a8 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -2744,7 +2744,8 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, > } > > struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > - bool *locked) > + bool *locked, > + struct cgroup *dst_cgrp) > __acquires(&cgroup_threadgroup_rwsem) > { > struct task_struct *tsk; > @@ -2784,15 +2785,28 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > tsk = tsk->group_leader; > > /* > + * RT kthreads may be born in a cgroup with no rt_runtime allocated. > + * Just say no. > + */ > +#ifdef CONFIG_RT_GROUP_SCHED > + if (tsk->no_cgroup_migration && (dst_cgrp->root->subsys_mask & (1U << cpu_cgrp_id))) { > + tsk = ERR_PTR(-EINVAL); > + goto out_unlock_threadgroup; > + } > +#endif > + > + /* > * kthreads may acquire PF_NO_SETAFFINITY during initialization. > * If userland migrates such a kthread to a non-root cgroup, it can > - * become trapped in a cpuset, or RT kthread may be born in a > - * cgroup with no rt_runtime allocated. Just say no. > + * become trapped in a cpuset. Just say no. > */ > - if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) { > +#ifdef CONFIG_CPUSETS > + if ((tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) && > + (dst_cgrp->root->subsys_mask & (1U << cpuset_cgrp_id))) { > tsk = ERR_PTR(-EINVAL); > goto out_unlock_threadgroup; > } > +#endif Nit: maybe move this #ifdefery out to a header? Thanks, Quentin
